To maximize the transmission capacity of an optical fiber transmission system, a single optical fiber may be used to carry multiple optical signals in what is called a wavelength division multiplexed system (hereinafter a WDM system). The multiple optical signals may be multiplexed to form a multiplexed signal or WDM signal with each of the multiple signals being modulated on separate channels. Each channel may be at an associated wavelength centered on a defined frequency grid, e.g. according to a channel plan established by the International Telecommunications Union (ITU). The range of wavelengths that may be transmitted on the system is known as the system bandwidth. Systems may utilize their system bandwidth to carry a desired number of channels with desired modulation format, channel plan and bit rate.
In a known configuration, an owner of an optical system may possess all necessary transmission equipment and sell a defined amount of capacity on the system to customers. For example, the owner might sell a defined number of channels at a defined bit rate and channel plan on the system. In such an arrangement, the owner of the system would control all aspects of the physical layer, including, for example, the system channel plan, the channel power, modulation format, bit rate, etc.
Recently, however, there has been interest in a system wherein the owner of the system would sell a defined portion of the system bandwidth to each customer. In this configuration, each customer would have partial control over the physical layer including the type and configuration of equipment used to transmit signals in their portion of the system bandwidth. Each customer would also have control over certain transmission characteristics within their portion of the system bandwidth. Different customers, for example, may establish different channel plans, modulation formats, bit rates, etc. within their portions of the system bandwidth. This overall system configuration gives customers control over adding, removing and/or reconfiguring services within their bandwidth and for managing loading in the unoccupied portions of their bandwidth.
A challenge associated with such a system is that physical layer changes made by one customer within their portion of the system bandwidth may affect transmission performance in other portions of the system bandwidth owned by other customers. For example, a customer may provide a contaminated input spectrum with broadband noise outside of their allocated bandwidth that impacts other customers. Also, since customers could drop or add channels at any time, the corresponding change in path average power, peak power and optical signal-to-noise ratio (OSNR) of surviving channels may fundamentally affect the Q-factor performance of other customers. On receiver side, the customers' receiving amplifier gain and OSNR may be affected by presence of other customer's data. In addition to performance issues, security issues may arise if a customer receives signals outside of their allocated bandwidth.